1. Technical Field
This disclosure relates to photolithography in the field of integrated circuit manufacture, and more particularly to a method for improving the etch resistance of photoresists used in such photolithography.
2. Background of Related Art
Photolithography is a commonly used technique in the manufacture of integrated circuits for use in computers and other such applications. In photolithography a photoresist layer is formed on a substrate such as, for example, a silicon wafer. The photoresist is then covered with a mask containing a pattern, in transparent and opaque areas, which is intended to be etched onto the substrate. The mask is then exposed to actinic radiation, such as ultraviolet light (UV), X-ray, electron beam, and the like, which is transmitted through the transparent areas of the mask to cause a chemical reaction in corresponding regions of the photoresist. In a negative type photoresist the radiation impacted areas of the photoresist become insoluble in a developing solvent. For example, the radiation can initiate cross-linking, chain growth, photocondensation, or other such reaction to cause a chemical change in the photoresist. In a positive type photoresist the radiation impacted areas become more soluble in a developing solvent. For example, the radiation can cause photodegradation of the photoresist molecular structure. After radiation exposure the photoresist is developed by exposure to the developing solvent which washes away the soluble portions of the photoresist to leave a pattern. After this patterning step an etching process is conducted wherein the substrate is exposed to an acid, for example in a wet etch process, or an ion beam, for example in a dry etch process. The areas of the substrate covered by the remaining photoresist remain unetched. Finally, the remaining photoresist is removed by a suitable solvent or other conventional removal methods, leaving the substrate with a pattern etched therein.
In order to develop more powerful microprocessors, more electronic components must be put into the chip. Since the physical area of the chip is limited this means that the patterns etched into the substrate must become finer with higher resolution. At the present state of technology the patterns are of such fineness that the wavelengths of light used to expose the photoresist have become an important factor, the shorter wavelengths producing a higher resolution image.
Another factor is the thickness of the photoresist layer. The thinner the photoresist, the sharper the image. However, as the photoresist becomes thinner it becomes less able to withstand the etching process.
A method is provided herein for producing a photolithographic structure. The method includes (a) providing a photoresist having a base resin containing protected active sites which upon deprotection provide reactive sites and a photoactive component which is responsive to actinic radiation; (b) applying the photoresist to a substrate; (c) exposing selectively patterned areas of said photoresist to an effective dose of said electromagnetic radiation; (d) exposing said photoresist to a developing agent to create a patterned photoresist; then (e) deprotecting protected active sites of the base resin to provide reactive sites; then (f) reacting the reactive sites resulting from step (e) with an etch protectant containing a silylating agent to incorporate the etch protectant into the structure of the base resin; and, (g) etching the substrate.
The method described herein advantageously improves the etch resistance of the photoresist while maintaining the sensitivity of the photoresist to the patterning radiation.